Oxygen Vacancy Regulation by Chlorine-Anion Doped Perovskite for Biomass Chemical Looping Gasification

Biomass chemical looping gasification (BCLG) is a promising and ecologically benign process for producing hydrogen-rich syngas. In this study, the alkaline earth metal (AEM)-based ferrite perovskites, AFeO3−δ (A = Ca, Sr, Ba), were synthesized by sol–gel method. Among them, SrFeO3−δ (SF) demonstrated a well-defined perovskite structure and significant reactivity toward biomass. To enhance BCLG performance, a chlorine-doped oxygen carrier, SrFeO3−δ−xClx, was developed by incorporating Cl– into oxygen sites using FeCl3·6H2O, allowing for precise control of oxygen vacancies and lattice oxygen. Characterization (EPR, XRD, XPS) indicated successful Cl– doping, which generated lattice distortion, enhanced charge compensation, increased Fe4+ concentration and lattice oxygen, and promoted the formation of oxygen vacancies. These changes improved the redox activity of the oxygen carrier. Fixed-bed BCLG experiments indicated that Cl– doping considerably enhanced carbon conversion and gasification efficiency. Under optimal conditions (950 °C, water injection rate of 30 μL·min–1, and O/B ratio = 2), SrFeO2.8−δCl0.2 (SFCl20) generated 1.50 Nm3/kg of gas with 84.23% syngas selectivity, exhibiting preferable performance in terms of carbon conversion (91.92%) and gasification efficiency (95.10%). The material retained structural integrity and redox stability throughout 15 cycles with negligible degradation. This study emphasizes chlorine anion doping by a simple sol–gel method as an effective tool for modifying oxygen vacancies and redox behavior in perovskite oxygen carriers, providing a platform for BCLG.